The mechanisms which underlie the selective vulnerability of various central nervous system structures to hypoxic-ischemic injury are studied in rats and cats subjected to standardized insult conditions. In rats, the insult consists of unilateral common carotid artery ligation combined with arterial hypoxemia with maintenance of normal blood pressure. In cats, bilateral common carotid artery ligation and basilar artery occlusion together with moderate arterial hypotension are employed. Regional cerebral blood flow is assessed by means of the 14C-antipyrine autoradiographic method. Regional brain glucose metabolism is measured autoradiographically by means of 14C-2-deoxyglucose, an incompletely metabolized glucose congener. In separate series of similarly treated animals, histological examination of the brain will be performed. Patterns of altered regional blood flow and metabolism are correlated with each other and with histological changes. The studies will help to differentiate intrinsic regional tissue vulnerability from local vulnerability secondary to regional blood flow impairments and will help to clarify to pathogenesis of the neuropathological changes in patients with hypoxic-ischemic brain injury.